An alkaline storage battery is a repeatedly chargeable and dischargeable battery and has been widely used as a power source for portable devices. In particular, a nickel hydrogen storage battery, which employs a hydrogen storage alloy as a negative electrode active material, has high energy density and is relatively environmentally clean. Therefore, a nickel hydrogen storage battery is becoming widespread as a main power source of various portable devices.
In a current collecting method in a nickel hydrogen storage battery, a bottomed cylindrical container, which contains an electrode assembly composed of positive and negative electrodes, serves as a negative electrode terminal, and a sealing plate insulated from the container serves as a positive electrode terminal. The positive electrode is integrated with the sealing plate through a lead to form a current collecting structure, and the negative electrode is in contact with an inner wall side of the bottomed cylindrical container at the outermost peripheral portion thereof to form a current collecting structure.
In order to increase the capacity of such a nickel hydrogen storage battery, a method has been proposed in which, the thickness of the negative electrode located at the outermost peripheral portion of a spirally wound electrode assembly composed of positive and negative electrodes and a separator is reduced to be less than that of the other portion (for example, see the publication of Japanese Patent No. 3056521).
A conventional example described in the above publication of Japanese Patent No. 3056521 is specifically described with reference to FIGS. 11 and 12. In an alkaline storage battery which is applied also to nickel hydrogen storage batteries, a strip-like negative electrode 101 and a strip-like positive electrode 102 are wound spirally with a separator 103 interposed therebetween to form an electrode assembly, and the electrode assembly is contained in a bottomed cylindrical container 104, whereby the alkaline storage battery is configured. The negative electrode 101 is disposed so as to occupy the outermost peripheral portion of the electrode assembly. An outermost peripheral portion 105 of the negative electrode 101 is in contact with the container 104, and the negative electrode 101 is configured such that the thickness of the outermost peripheral portion 105 thereof is less than that of the other portion 106 (specifically, being 50% to 90%). The length L of the outermost peripheral portion 105 of the negative electrode 101 is substantially the same as the inner peripheral length of the container 104, and a boundary portion 107 is formed between the outermost peripheral portion 105 and the other portion 106.